Digital Pathology refers to the creation, viewing, management, sharing, analysis, and interpretation of digital images of sample slides comprising biological material (e.g. tissues) and includes workflow considerations unique to a digital imaging environment. An important performance aspect of digital pathology is the quality of the digital images. For example, some digital images may have a weak contrast, when the sample slides comprise unstained biological material, such as unstained tissue. The weak contrast may affect the readability of the digital images and thus make it difficult for e.g. automatic registration by a computer algorithm. For example, U.S. Pat. No. 8,229,194 B2 describes an image registration method.